A forced-air heating, ventilation and air conditioning system depends on a system of ducts to provide a controlled path for distributing heated or cooled air throughout the home. Typically, HVAC duct systems are made of sheet metal, but other rigid heatproof materials such as fiberglass or insulated plastic may be used.
Air ducts require periodic cleaning and maintenance in order to maintain acceptable indoor air quality. Cleaning may be part of preventive maintenance or it may be required to improve performance of the HVAC system. It may also be required to reduce or control micro-organisms. Micro-organisms can pose a health threat to people with allergies and patients in medical facilities with exposed wounds.
Duct systems are difficult to clean. Duct systems are very difficult to clean effectively. Duct systems are expensive to clean. Duct systems with flexible ducts are difficult to clean with conventional large scrubbing brushes. Duct systems used in general commercial applications must be maintained with some regularity. Duct systems used in specialized applications with specific requirements, such as healthcare facilities, will have more stringent maintenance requirements. Duct systems used in food preparation applications will have different maintenance requirements due to the combustion risks associated with grease build up. Restaurant kitchen stove/range hood vents and ducts are generally installed vertically, yet still accumulate considerable amounts of grease. A grease duct is a duct that is specifically designed to vent grease-laden vapors from commercial cooking equipment such as stoves, pizza ovens, deep fryers and woks to the outside of a building or mobile food preparation trailer. Grease ducts are regulated both in terms of their construction and maintenance, forming part of the building's passive fire protection system. Even the cleaning schedule is typically dictated by the fire code and evidence of compliance must be kept on file by the owner.
U.S. Pat. No. 4,101,700 to Ray et al. for “Thermally Insulating Duct Liner” discloses a flexible thermally insulating duct liner comprising a fibrous thermal insulation layer having an organic fibrous layer having an open structure bonded to its working face, the working face being thereafter coated with a flame retardant vinyl polymer containing coating. This duct liner is intended to be inserted into ducts, but does not disclose multiple layers which can be removed serially.
U.S. Pat. No. 7,140,396 to Mota et al. for “Air duct containing an organic liner material” discloses an air duct suitable for conducting a flow of air. The air duct includes a central layer formed from fiber glass. The central layer has an inner surface and an outer surface. The air duct also includes a liner layer arranged adjacent to the inner surface of the central layer. The liner layer is formed from an organic material and is substantially free of fiberglass, or is formed from polyester and rayon. The central layer and liner layer are arranged to define a channel for conducting a flow of air. While the duct liner is comprised of multiple layers, the multiple layers comprise a single duct liner, rather than multiple duct liners.
U.S. Pat. No. 4,573,715 to Armbruster for “Temporary duct liner interconnect device” discloses a duct liner interconnecting device for temporarily interconnecting the ends of sections of duct liner includes a pair of complementary semi-cylindrical elements hinged together along one edge for movement from an open position in which the elements are side by side to a closed position in which the elements form a short tubular member with a longitudinal channel to receive the ends of duct liner sections to be interconnected, a pair of arcuate spring clips pivotally attached to one of the elements releasably latch the elements together in the closed position, and a tapped aperture in one of the elements receives a lubrication fitting to allow the introduction of lubricant into the duct liner to facilitate pulling of lightguide cable through the duct liner.
U.S. Pat. No. 5,762,109 to Matthews et al. for “Duct with replaceable insulating duct liner and method of maintaining the same” discloses a duct for gas flow applications with a replaceable insulating duct liner that can be axially inserted into and removed from a tubular shell of the duct. Preferably, the replaceable insulating duct liners comprise fibrous and/or cellular insulation materials. Duct systems using duct sections with replaceable insulating duct liners can be maintained by removing duct sections from the system; removing the replaceable insulating duct liners from the duct sections; inserting new replaceable insulating duct liners into the duct sections; and replacing the duct sections into the duct system. This duct liner is intended to be inserted into ducts, and is removable, but does not disclose multiple duct liners which can be removed serially.
U.S. Patent Application No. 20130295303 to Parks et al. for “Duct Liner” discloses a duct liner that includes an insulation layer and a facing. The insulation layer having a first edge surface, a second edge surface that is spaced apart from the first edge surface, and a first and second face surfaces that extend from the first edge surface to the second edge surface. The facing is disposed on the first face surface, such that the first face surface is entirely covered by the facing. The facing is disposed on the first and second edge surfaces, such that the first and second edge surfaces are entirely covered by the facing. Two spaced apart strips of the facing are disposed on and cover a portion of the second face surface adjacent to the first and second edge surfaces, such that a portion of the second face surface between the strips is uncovered by the facing.
U.S. Patent Application No. 20060070521 to Stark et al. for “Removable duct liner” discloses a porous polymeric membrane layer and, optionally, a support layer, in which the article is a duct liner adapted to be removably positioned within a porous air duct. The liner may also be used in conventional metal and plastic ducts to reduce cleaning frequency. In another aspect, the invention is a porous air duct comprising: a liner comprising a porous polymeric membrane and, optionally, a support layer; and an openwork conduit, said liner disposed within the openwork conduit. This duct liner is intended to be inserted into ducts, and is removable, but does not disclose multiple duct liners which can be removed serially.
U.S. Patent Application No. 20070295422 to Ostan et al. for “Flexible Sleeve Liner for a Convolute Duct” discloses an air induction system wherein the outlet air assembly includes a sleeve-lined convolute duct. A sleeve liner is disposed within a convolute duct which spans the convolutes, wherein an attached end of the sleeve liner is attached to a non-convolute portion of the convolute duct, wherein a free end is freely slidable in the convolute duct, and wherein the free end of the sleeve liner and the attached end of the sleeve liner each serve as a sealing cuff whereby air flow is laminar throughout irrespective of the convolutes.
While the art describes various implementations of removable duct liners wherein the duct liners can be removed and replaced with a new duct liner, what is needed is a multi-layer duct liner wherein a single multi-layer duct liner can be installed, and then layers of the multi-layer duct liner can be removed as they are used, saving time and effort required to install a new duct liner.